My invention relates to vehicle suspensions and particularly relates to a modification of a spring assembly for vehicles, whether the vehicles are on-road, off-road, or all-terrain vehicles.
Many vehicle suspensions have a piston-and-cylinder type shock absorber mounted between the vehicle frame and a moveable suspension member. This suspension member is typically a rocker arm pivoted to the frame of the vehicle, or to the axle. The shock absorber allows the suspension member only a limited range of movement so that frequently, especially when the vehicle is travelling over rough terrain, the shock absorber repeatedly reaches the limits of its stroke. At the limits of its stroke the shock absorber or a suspension member makes contact with a bump stop device to restrict further motion in that direction.
When the vehicle is travelling while fully loaded, the shock absorber tends to be repeatedly compressed to its minimum-length configuration. On the other hand, when the vehicle is travelling while unloaded, the vehicle body has a greater tendency to rebound upward after experiencing road or terrain shocks, and consequently the shock absorber tends to be extended to its maximum-length configuration. When the shock absorber reaches its maximum or minimum length configuration, it loses its ability to cushion the vehicle from shocks caused by over-road or over-terrain travel. Consequently, passenger fatigue and discomfort are aggravated, and the vehicle cargo and suspension are more easily damaged.
The problems above described are most likely to occur when the mission requirements for existing vehicles change so as to necessitate their carrying of larger loads or traversing more difficult terrain than originally intended. In other cases, a relatively newly designed military vehicle will have been mass produced and be in service all over the world before it is realized that the vehicle suspension is being worn excessively because of the vehicle spring design. In one particular military vehicle known as a High Mobility Multipurpose Wheeled Vehicle (HMMWV or "humvee",) the limited shock absorber stroke has led to unacceptable amounts of wear or breakage in the ball joints connecting wheel assemblies to the vehicle suspension.
One possible solution to the above problem is simply to retrofit vehicles with stiffer springs or higher capacity shock absorbers. However, this solution would make the suspension insensitive to low level shocks or bumps the vehicle receives during over-the-road travel and would thus not afford optimal protection for the vehicle, cargo and passengers. Another possible solution is to retrofit vehicles with variable-pressure pneumatic shock absorbing equipment. However, this would involve the expense of retrofitting vehicles with air pumps and air lines as well as the shock absorbing units themselves. For military vehicles, it would be necessary to modify the vehicles so that the pumps and lines are not vulnerable to enemy fire. This would add to the cost of retrofitting military vehicles with pneumatic shock absorbing means.
My invention is a structure which modifies the existing suspension springs on a military vehicle. In the preferred embodiment, the structure comprises a set of plates having tapered edges insertable between the coils of the spring. When the spring expands or contracts beyond a predetermined limit, the plates engage the coils so as to stiffen the spring. The plates can be spaced or dimensioned to engage the coils sequentially as the spring contracts, thereby stiffening the spring in a progressive, stepwise fashion. The plates are moveable perpendicularly toward or away from the longitudinal axis of the spring to vary the width of the tapered plate portion sandwiched between the coils when the spring compresses. This plate movement is a further means to control the degree to which my spring modification structure changes the stiffness of the spring.